Aasimar

Aasimar are a player character race in Dungeons And Dragons editions 2, 3 and 3.5, and in Pathfinder. They are counterparts to Tieflings and Genasi, being mortals who bear the blood of Celestials - the residents of the Upper Planes - in their lineage.

Aasimar originated in the Planescape setting, as with their counterparts. Like the Genasi, though, they came after the setting was initially released; the corebook for Planescape introduced only the Tiefling, Githzerai and Bariaur races.

Aasimar are basically tailor made for people who want to play the various Good branches of the Alignment tree, especially as Clerics or Paladins, since they literally have living good in their veins. Despite this, or perhaps because of it, Aasimar have never been the most popular of races, even in Planescape; players generally pick their counterparts instead.

In 4e, because of this lack of popularity, and to pointedly avoid "grid-filling", Aasimar never made it over. Instead, Devas, beings who are former angels banished or voluntarily departed from the Astral Sea to live amongst mortals, took their place.

In Pathfinder, it's noted that a lot of Aasimar actually tend to go evil either because superstitious yokels tend to pile on emotional trauma and guilt until they snap by constantly harassing them for "blessings" that the aasimar can't actually give, or because they realize everyone automatically expects them to be capital-G Good Guys/Girls and so they can easily manipulate people. This is yet another way in which Pathfinder likes to present itself as the GrimDark D&D equivalent setting.